Rapid thermal carbonization in a dilute acetylene (C2H2) atmosphere has been used to chemically modify and precisely tune the pore size of ultrathin porous nanocrystalline silicon (pnc-Si). The magnitude of size reduction was controlled by varying the process temperature and time. Under certain conditions, the carbon coating displayed atomic ordering indicative of graphene layer formation conformal to the pore walls. Initial experiments show that carbonized membranes follow theoretical predictions for hydraulic permeability and retain the precise separation capabilities of untreated membranes.

We have shown a new method for carbon deposition on silicon that results in the growth of graphene layers inside of the pores of pnc-Si. Very precise control (˜nm resolution) of pore sizes is obtainable by the technique. Interestingly the modified membranes do not exhibit enhanced water flow despite similarities to carbon nanotube membranes that are known to exhibit enhanced flow. It has also been demonstrated that carbonized membranes exhibit high resolution separations and high hydraulic permeabilities as seen with unmodified pnc-Si in Gaborski et al.